The present invention relates to a fuel injection system for injecting the fuel into an internal combustion engine of the spark ignition type.
There have been developed heretofore many and various types of fuel injection systems for the internal combustion engines of a spark ignition type. One type of the generally employed fuel injection systems is provided with a fuel metering device for metering a continuously flowing fuel, depending upon intake flow rates of air inducted into the engine, and a fuel through the fuel metering device is sequentially injected through fuel injection nozzles attached to the intake pipe or duct of the engine. In a fuel metering device proposed heretofore, a variable orifice is located in a fuel passage and operatively coupled to a sensor for detecting an intake air flow rates inducted into the engine. In addition, the fuel metering device comprises a differential pressure regulating valve for maintaining constant the difference in pressure across the variable control orifice. In this manner, the variable orifice precisely controls a flow rate of a fuel which flows continuously through a fuel passage.
In another known type of the fuel injection system, a fuel is metered by a Jerk type fuel injection pump provided with a solid cam control device which is actuated in response to rotational speeds of the engine and depending upon the degree of opening of a throttle valve, whereby a fuel-air ratio is controlled. A fuel metered is intermittently injected through a fuel injection nozzle into each cylinder of the engine.
The hitherto known fuel injection systems however suffer from various drawbacks. For example, in the case of the first mentioned type of the fuel injection system, unburnt fuel will flow out from an exhaust port to increase the content of HC in an exhaust gas when the air intake valve is opened simultaneously with the exhaust valve as is common in the internal combustion engine of the spark ignition type, since a fuel is continuously supplied to the injection valves of the individual cylinders from the fuel control apparatus during engine operation. On the other hand, the last mentioned injection pump of the Jerk type has an advantage that a fuel can be effectively atomized due to the fuel injection effected at a high pressure. However, since control of a fuel flow rate injected into the engine is carried out indirectly by detecting a rotational speed of the engine and opening of the throttle instead of detecting directly a flow rate of intake air, a fuel-air ratio will be undesirably degraded when the flow rate of intake air is varied due to the dimensional errors or tolerance of the mechanical connecting portion or abrasion in the engine. In addition, in the case of the multi-cylinder engine, a Jerk type injection pump requires the same number of elements as that of the cylinders in the engine, which involves complicated structure of the fuel injection system. Further, many components of the injection pump require a high precision working which is necessarily accompanied with high cost. Moreover, the large and heavy structure of this injection pump makes difficult the installment thereof onto a vehicle